This invention relates to improvements in the structure of ignition systems for internal combustion engines. More particularly, the present invention relates to an improved ignition system for an internal combustion engine in which circuits for detecting the level of spark energy supplied to the spark plugs in the engine and controlling the value of primary current of the ignition coil on the basis of the result of energy level detection are additionally provided so that spark energy of predetermined level can be supplied to the spark plugs in the engine.
It is known that, in a prior art ignition system for an internal combustion engine, the duration of secondary current flowing through the ignition coil is detected to control the value of primary current supplied to the ignition coil so that the secondary current duration can be controlled or maintained at a predetermined length of time. It is also known that, in another prior art ignition system having a concern with the aforementioned one, the detected value of secondary current is integrated to calculate the area, and the value of primary current is controlled on the basis of the calculated area so that the integrated amount of secondary current can be controlled or maintained at a predetermined setting. However, in both of these prior art ignition systems, the spark energy cannot always be accurately detected since the secondary current is only detected. It has therefore been difficult for these prior art ignition systems to strictly meet the operation requirements of the engine when an excess or shortage of spark energy results from, for example, a variation of the secondary voltage.